Dynamical Jahn-Teller effect and antiferromagnetism in Cs3C60.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• The Jahn-Teller effect is crucial for understanding distortions in molecules with degenerate electronic states.
• Fullerides, like Cs(3)C(60), exhibit complex electronic and magnetic properties influenced by electron-phonon coupling.
• Investigating the dynamical Jahn-Teller effect is key to elucidating magnetic interactions in these materials.

Purpose of the Study:

• To investigate the dynamical Jahn-Teller effect on fullerene sites in insulating Cs(3)C(60) using ab initio methods.
• To determine the nature of vibronic excitations and their contribution to Jahn-Teller stabilization.
• To establish an exchange model explaining the magnetic properties and Néel temperature.

Main Methods:

• Fully ab initio electronic structure calculations.
• Vibronic excitation analysis.
• Derivation of a spin-exchange model.

Main Results:

• Vibronic excitations of rotational type were found at energies greater than or equal to 65 cm(-1).
• The kinetic contribution to Jahn-Teller stabilization energy is approximately 90 meV.
• Free rotations of deformations occur independently on each C(60), destroying orbital ordering and establishing exchange interactions.

Conclusions:

• Intermolecular interactions do not localize distortions in Cs(3)C(60).
• The derived exchange model accurately predicts the Néel temperature for A15 Cs(3)C(60), aligning with experimental values.
• The study confirms conventional S = 1/2 exchange interactions on fullerene sites due to the dynamical Jahn-Teller effect.